A. Technical Field
The present invention relates to a hydrophilizing agent and a hydrophilized fiber treated with the agent.
Specifically, the present invention relates to a hydrophilizing agent which is ideal for fibers that are to be processed into nonwoven fabrics and formed into fiber products such as topsheets for disposable diapers and sanitary napkins, and also relates to hydrophilized fibers treated with the agent. More specifically, the present invention relates to a hydrophilizing agent which not only imparts hydrophilicity, but also prevents a phenomenon referred to as “wet back”, i.e., rewetting a wearers' skin by the reverse flow of urine or body fluid through topsheet after it is absorbed through the topsheet, and improves the liquid absorbing performance and durable liquid permeability of the topsheet; and also relates to a hydrophilized fiber treated with the agent.
B. Background Art
Absorbent articles such as disposable diapers and sanitary items usually comprise three components: a topsheet, a water-repellent back sheet, and a core of pulp and/or absorbent polymers enclosed between the topsheet and the backsheet; wherein the topsheet is manufactured by imparting liquid permeability (hydrophilicity) to nonwoven fabrics formed primarily of hydrophobic fibers, such as polyolefin fiber or polyester fiber including triacetate fiber. The topsheet is usually treated with a hydrophilizing agent so as to make the topsheet hydrophilic.
When urine or body fluid is absorbed into an absorbent core through the topsheet, the topsheet is required to have excellent liquid permeability, in other words, the liquid must be absorbed into the internal absorbent core completely through the topsheet in a short amount of time, for the purpose of minimizing a wet feel on the topsheet surface. In addition, the liquid absorbed in the absorbent core must not flow back to the topsheet surface. A hydrophilizing agent, which is easily flushed off from the topsheet after one or two times of liquid absorption and thus result in a drastic decrease in the topsheet's liquid permeability is not preferable, because absorbent articles containing this type of topsheet should be changed frequently. Thus, the hydrophilizing agent must attain durable liquid permeability of the topsheet, and retain the durable liquid permeability of the topsheet for a long period of time, in other words, minimize the time-dependent deterioration of the durable liquid permeability of the topsheet.
For smooth manufacturing of nonwoven fabric, fibers treated with the hydrophilizing agent must have sufficient antistaticity and good processability in carding in order to be processed into a uniform web without fiber wrapping onto a card cylinder.
For the wearing comfort of absorbent articles, they must retain excellent liquid permeability with minimum wet back, and also retain sufficient hydrophilicity (durable liquid permeability) after repeated liquid permeation. It is well known that those performances are improved with a hydrophilizing agent. For example, Patent Reference 1 proposes a method for treating fiber with a potassium C12-22 linear alkyl phosphate. Patent Reference 2 proposes a hydrophilizing agent formulated by blending a C10-30 alkyl phosphate salt with a C10-30 betaine compound, a sulfate salt, or a sulfonate salt. Patent Reference 3 proposes a method in which an alkyl phosphate salt is blended with a polyether-modified silicone. Patent Reference 4 proposes a method including the step of blending two betaine compounds to an alkyl phosphate salt.
Patent Reference 5 proposes a method including the step of blending a cationized compound of an acylated polyamine, an alkylphosphate salt, a trialkyl glycine derivative, and a polyoxyalkylene-modified silicone to a polyoxyalkylene fatty acid amide. Patent Reference 6 proposes a method including the step of treating fiber with a blend of an alkylphosphate salt, a trialkyl glycine derivative, a polyoxyalkylene-modified silicone, and an alkoxylated ricinoleic compound.
[Patent Reference 1] JP B 63-14081
[Patent Reference 2] JP A 60-215870
[Patent Reference 3] JP A 4-82961
[Patent Reference 4] JP A 2000-170076
[Patent Reference 5] JP A 2002-161474
[Patent Reference 6] JPA2002-161477
The methods proposed in these references contain both advantages and disadvantages with respect to the required surface properties of nonwoven fabrics, and none of those methods sufficiently prevents wet back. A hydrophilic agent is preferable for improving liquid permeability, while a hydrophobic agent is preferable for minimizing wet back. Such a situation suggests that nonwoven surface properties are not only influenced by the hydrophilic and hydrophobic properties of the components in a hydrophilizing agent, but also influenced by the chemical structure thereof, the balance between hydrophilicity and hydrophobicity of the components thereof, and the interaction between the components thereof. It has been difficult for one hydrophilizing agent to attain both improved liquid permeability and wet back prevention simultaneously, and minimize the time-dependent deterioration of durable liquid permeability. Thus, wet back has been prevented by some type of means for modifying the structure of absorbent articles, such as forming a double-layered nonwoven topsheet comprising nonwoven fabrics having different hydrophilic properties, or adjusting the arrangement and amount of pulp and/or absorbent polymers.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved hydrophilizing agent, which functions to decrease the amount of wet-back liquid without modifying the structure of absorbent articles in which it is used, and imparts good processability in carding to fibers and superior durable liquid permeability to a fiber assembly, as well as a need for improved hydrophilized fiber treated with the agent.